Machines, such as wheel loaders, typically include a linkage assembly which mechanically connects an implement (e.g., a bucket) to a frame of the machine. Linkage assemblies, such as so-called “eight-bar linkages,” will typically include a lift arm having one end connected to the frame and the opposite end coupled to the implement. Generally, the linkage assembly also includes a number of mechanical links and/or levers and hydraulic actuators coupled to the frame and the lift an such that the lift an and the implement can be moved relative to the frame.
During operation of the machine, the linkage assembly is subjected to various loads and forces, some of which may be severe. Therefore, it is critical that each component thereof has sufficient structure and connection to one another to provide the strength necessary to withstand these loads and forces. Linkage assemblies have traditionally been constructed to be relatively large and bulky in order to accommodate such loads and forces.
Lift arms of an eight-bar linkage assembly in such machines are generally of a so-called “box-boom” construction or a plate construction. Box-boom lift arms are formed of a plurality of metal plates disposed in a box arrangement with a generally rectangularly shaped traverse cross-section and a generally hollow interior. The arrangement of U.S. Pat. No. 6,409,459 to Ginn et al., which is assigned to the assignee of this disclosure, includes such a boom lift arm. A box-boom lift arm typically includes one or more openings to accommodate other components, such as links, levers, or hydraulic actuators, extending through the upper or lower plates of the box-boom. The arrangement of the '459 patent includes a rear tilt lever that extends through an opening in the box boom lift arm. The rear tilt lever is pivotably coupled to the boom lift arm such that the opposite ends of the rear tilt lever pivot about the pivot axis on the boom lift arm. One end of the rear tilt lever is coupled to the machine frame by a rear tilt link, and the other end of the rear tilt lever is coupled to a tilt actuator, which is further coupled to the implement by way of a front tilt lever. Actuation of the tilt actuator causes the tilting of the implement in either direction.
In contrast, a lift arm of a plate construction includes a pair of side plates that are secured together by stabilizing front and/or rear cross-members. Eight-bar linkages including lift arms of a plate construction typically include two complete sets of tilt components, that is, two rear tilt levers, two rear tilt links, two tilt actuators, and two front tilt levers. The separate sets of tilt components have the same general relationship to one another as those described with regard to the box boom arrangement above, but one set of tilt components is coupled to one of the side plates of the lift arm, while the other set of tilt components is coupled to the other of the side plates of the lift arm. In other words, the rear tilt levers are coupled at the first ends to the frame by respective rear tilt links. The opposite ends of the rear tilt levers are coupled to respective tilt actuators, which are in turn coupled to the implement, generally through respective front tilt levers. The intermediate portions of the rear tilt levers are pivotably coupled to the respective plates of the lift arm.
An operator, typically located in a cab on the machine, causes the linkage assembly to move through a range of motion to place the implement in desired positions. Unfortunately, the components of the linkage assembly tend to obstruct the view of an operator running the machine. A “box-boom” lift arm essentially blocks the view of at least the area opposite the boom from the operator inasmuch as it presents a moving, elongated box. While a boom having a plate construction may provide a somewhat enhanced view over a boom having a box construction, the stabilizing front and/or rear cross-members of a plate construction boom are themselves quite bulky and obtrusive in order to accommodate the forces and loads. Moreover, the pairs of rear tilt levers, tilt actuators, rear tilt links, and front tilt levers generally utilized with a lift arm of a plate construction likewise obscure the areas in front of and to the side of the plates of the lift arm. As a result, the components of linkage assemblies including a plate-construction lift arm likewise typically obstruct the view of the operator through and around the linkage assembly. Obstructions in an operator's view of the area in front of and to either side of the implement and around the linkage assembly can not only inhibit efficient and effective operation of the machine, but can also present safety concerns, particularly where the arrangement may present relatively large blind spots to the operator.
It is therefore desirable to provide a linkage assembly that provides an operator with an enhanced view of the area around and in front of an associated machine, while exhibiting the structural integrity necessary to withstand the loads and forces associated with use of such a machine. The present disclosure is directed to overcoming one or more of the problems set forth above.